1. Field of the Invention
The present invention relates generally to incremental fault dictionaries, and more particularly pertains to an incremental fault dictionary in which the diagnostic simulation results of current tests are stored for future use.
Diagnostic simulation results are incrementally added to the incremental fault dictionary, and information therein is used to avoid expensive redundant fault simulations. The size of the incremental fault dictionary is maintained within user definable bounds by identifying and deleting faults that need not be maintained in the incremental fault dictionary. The incremental fault dictionary beneficially provides more accurate and faster diagnostics than a typical prior art diagnostic fault simulation.
2. Discussion of the Prior Art
The use of fault dictionaries is well documented in the literature (see, for example, xe2x80x9cDiagnosis and Reliable Design of Digital Systems,xe2x80x9d by Melvin A. Breuer and Arthur D. Friedman.) A fault dictionary is a large table that lists for each test pattern and each fault from some master fault list how the response of the design with that fault present differs from the response of the fault-free design. The dictionary is generated prior to diagnosing an IC, and is used to compare the observed behavior of the IC with the stored behaviors of the same with any of the faults listed in the dictionary. It is static in the sense that, once generated, no further information is added.
The main problem with prior art static fault dictionaries is that they are typically so large that they cannot be stored in a reasonable size memory or be made accessible in a reasonable manner. The present invention avoids the size problem by storing and retaining in an incremental fault dictionary only that information and data that has proven to be useful.
Accordingly, it is a primary object of the present invention to provide an incremental fault dictionary which beneficially provides more accurate and faster diagnostics than a typical prior art diagnostic fault simulation, and an incremental fault dictionary which optimizes diagnostic simulation performance versus space consumed by the incremental fault dictionary.